This application claims the priority benefit of Japanese application serial no. 2001-287021, filed on Sep. 20, 2001, and 2002-078952, filed on Mar. 20, 2002.
1. Field of the Invention
This invention relates in general to an image forming device, such as a copying machine, a printer, or a facsimile. More particularly, the invention relates to a tandem type image forming device, wherein after a first transfer stage at which a toner images on plural image supporters disposed along an intermediate transfer belt are sequentially composed on the intermediate transfer belt at a first transfer section where the intermediate transfer belt and each image supporter are oppositely arranged, the composite toner image transferred on the intermediate transfer belt is collectively transferred on a transfer material at a secondary transfer section where the intermediate transfer belt and the transfer material are oppositely arranged.
2. Description of Related Art
As described above, the tandem-type image forming device has the following advantages. A large amount of color documents were handled and this would continue in increasing volume for many more years, and therefore, demands for a compact and high-speed image forming device, such as a full color printer and a full color copying machine, etc. is highly desirable
For the color image forming device, in general there are two types, namely, a one drum type image forming device and a tandem type image forming device. The color image forming device of one drum type comprises a plurality of developing units disposed around one photoreceptor (the image supporter) for forming toner images in different colors. Thereafter, a composite toner image is formed on the photoreceptor by using the developing units, and then the composite toner image on the photoreceptor is transferred onto a recording medium, such as a paper or an OHP sheet, to form a color image. On the other hand, tandem-type color image forming device comprises a plurality of image forming units each of which includes a photoreceptor and an image forming means. The single-color toner image for each color is respectively formed on each image forming unit. These single-color toner images are overlapped and transferred onto a recording medium transported by a transferring/transporting belt, or onto an intermediate transfer belt, so as to form a composite color image.
The one drum image forming device can be more compact since one photoreceptor is included, and advantageously, the cost can be reduced. However, because one photoreceptor is usedperform for several times (usually, 4 times) of image forming processes to form a full color image, therefore the image formation with a high speed is very difficult. In contrast, the tandem-type image forming device has drawbacks in being large in size and high cost, but has advantages in the image formation with a high speed. Recently, since the need for a high speed or a faster and full color forming device is highly demanded, skilled people pay more attention on the above tandem-type image forming device.
For the tandem-type image forming device, there are a direct transfer type and an indirect transfer type. The tandem-type image forming device of direct transfer type transfers sequentially the image on the photoreceptor of each image forming unit onto the recording medium that is transported by the transferring/transporting belt. On the other hand, for the tandem-type image forming device of indirect transfer type, a first transfer stage is first performed so that the image on the photoreceptor of each image forming unit is sequentially overlapped onto the intermediate transfer belt. Next, the secondary transfer stage is performed so that the first transferred image on the intermediate transfer belt is wholly transferred onto the recording medium.
Referring to FIGS. 17 and 18, generally, in the tandem-type image forming device of direct transfer type, each of the image forming units is disposed side by side in the horizontal direction along the transferring/transporting belt. In this way, the paper feeding device for feeding the recording medium is disposed at the upmost upstream side of the transferring/transporting belt. Therefore, the perimeter of the horizontal portion where the recording medium on the transferring/transporting belt is transported gets longer, but however such a image forming device has a drawback, in that the device main body gets larger along the horizontal direction.
In order to prevent the device main body from becoming large along the horizontal direction, it is necessary that the fixing device has to be disposed in the vicinity of a separating section at which the recording medium where the composite toner image is transferred thereon is separated from the transferring/transporting belt. However, in such a configuration, it is very difficult to maintain a sufficient gap at which the recording medium that is separated from the transferring/transporting belt possesses a margin to bend between the separating section and the fixing device.
Therefore, in the above structure where the separating section and the fixing device are formed nearby, it is easy that the transferred image is adversely affected by an impact when the tip of the recording medium enters the fixing device (the thicker the recording medium is, the larger the impact is), or by a speed difference between the fixing device""s transporting speed and the transferring/transporting belt""s transporting speed. In contrast, in the tandem-type image forming device of intermediate transfer type, the position of the secondary transfer device can be more freely selected. Therefore, in the tandem-type image forming device of intermediate transfer type, the paper-feeding device and the fixing device can be disposed under the intermediate transfer belt, and advantageously, the device main body can be more compact along the horizontal direction. In addition, the device can maintain a sufficient gap at which the recording medium that is separated from the intermediate transfer belt can be bent between the fixing device and the separating section of the intermediate transfer belt. As described, since the tandem-type image forming device of intermediate transfer type possesses a margin capable of disposing the fixing device, it almost has no influence on the image formation of fixing device. For reasons as described above, skilled people in the field have paid much attention on the tandem-type image forming device of intermediate transfer type.
In the aforementioned image forming device, after the composite toner image on the intermediate transfer belt 10 of the secondary transfer device is collectively transferred on the transfer S, it is necessary to exactly separate the transfer paper S from the intermediate transfer belt 10 at the separating section. The separating ability of the transfer paper S at the separating section is also affected by the material of the intermediate transfer belt 10 and the entrance angle of the recording medium (the transfer paper S), but is largely affected by the winding angle xcex8 with respect to the supporting roller 16 of the intermediate transfer belt 10 at the separating section. If the intermediate transfer belt 10""s the winding angle xcex8 with respect to the supporting roller 16 forming the separating section is small, the separating ability of the transfer paper S at the separating section gets worse. In the worst situation, the transfer paper is not separated at the separating section, and then is transported and gets wounded on the intermediate transfer belt 10. Therefore, for the image forming device using the intermediate transfer belt 10, it is necessary to form a separating charger or a separating claw in order to separate the transfer paper S smoothly at the separating section according to the conventional art.
In order to improve the separating ability of the transfer material at the separating section of the intermediate transfer belt, the present inventor provides an image forming device (as shown in Japanese Laid Open No. 08-146706) with a structure that the toner image supporting surface of the intermediate transfer belt between the first transfer device and the secondary transfer device is bent by a bending member to the inner surface side of the intermediate transfer belt.
According to the above image forming device, since the toner image supporting surface of the intermediate transfer belt is bent by a bending member to the inner surface side of the intermediate transfer belt, a sufficient winding angle of the intermediate transfer belt with respect to the separating roller can be obtained. Therefore, in the image forming device, the transfer material at the separating section of the intermediate transfer belt can be smoothly separated, and the separating charger or the separating claw to help the curvature separation for the transfer material is not necessary.
On the other hand, in the tandem-type image forming device of intermediate transfer type using the intermediate transfer belt, when the composite toner image is transferred to the transfer material at the secondary transfer device, a portion of toner of the composite toner image is not transferred to the transfer material and then is residual on the intermediate transfer belt. After the secondary transfer stage, in order to avoid influence on the next image formation, the residual toner on the intermediate transfer belt has to be removed from the intermediate belt at least before reaching the first transfer device.
In image forming device disclosed in Japanese Laid Open No. 2000-137386, a cleaning device for removing the residual toner on the intermediate transfer belt after the secondary transfer is disposed at the downstream side of the secondary transfer device and at the upstream side of the pressing member (used as the above bending member). In general, the cleaning blade or the cleaning brush is used as most of the cleaning devices.
FIG. 19 shows an image forming device disclosed in Japanese Laid Open No. 2000-137386. The image forming device comprises a driving roller 14, driven rollers 15, 16, an intermediate transfer belt (belt, hereinafter) 10 and a bending roller 150. Referring to FIG. 19, since a portion of the outer surface of the belt 10 is bent by the bending roller 150, the space occupied by the belt device is reduced. Therefore, the degree of freedom of the machine layout disposed in the vicinity of the belt device is increased. For example, referring to FIG. 14, the portion of the belt device, which is bent by the bending member, can be used for arranging the fixing device 25, so that the image forming device can become more compact.
Additionally, in the image forming device shown in FIG. 19, four image forming units 18 are arranged along the belt outer surface of the intermediate transfer belt 10. Each image forming device 18 comprises a photoreceptor 40 (used as the image supporter) and an image forming means for forming a toner image on the photoreceptor 40. The image forming means comprises a charging roller 60, an exposure device 21, a developing device 67 and a photoreceptor cleaning device 63, etc.
In FIG. 19, the toner images for colors, such as cyan, magenta, yellow and black are respectively formed on each photoreceptor 40. The toner image of each color formed on the photoreceptor 40 is sequentially transferred to be overlapped on the intermediate transfer belt 10 by the first transfer rollers 62 that are disposed opposite to the photoreceptors 40. In this way, a full color composite toner image is formed on the intermediate transfer belt 10. The composite toner image formed on the intermediate transfer belt is then transferred onto the transfer paper S in a secondary transfer stage by a secondary transfer roller 23 that is disposed opposite to the outer surface of belt 10 stretched by the supporting roller 16. After the transfer paper S is separated from the belt 10 and then sent to the fixing device 25, the composite toner image that is transferred on the transfer paper S is fixed on the transfer paper S. On the other hand, the residual toner, which is not transferred onto the transfer paper S in the secondary transfer stage and is residual on the intermediate transfer belt 10, is further removed from the intermediate transfer belt 10 by the belt cleaning device 17 disposed at the secondary transfer device""s downstream side in the belt""s rotational direction. The belt cleaning device 17 is used to remove the residual toner on the intermediate transfer belt 10 by a cleaning blade 17a that is in contact with the belt 10""s outer surface. In addition, the belt cleaning device 17 is disposed at the bending roller 150""s upstream side in the belt""s rotational direction. In this way, the residual toner on the belt can be prevented from being adhered on the bending roller 150.
However, in the tandem-type image forming device of intermediate transfer type using the above intermediate transfer belt, unevenness of the perimeter of the intermediate transfer belt is created after a long time use. For example, when the initial perimeter of the intermediate transfer belt is 950 mm (23xc2x0 C.), the belt perimeter itself has a tolerance of about xc2x12 mm. In addition, due to the use environment (10xc2x0 C.xcx9c32xc2x0 C.), a contraction and expansion amount of about xc2x12 mm can be foreseen. Furthermore, the belt""s the expansion amount of about 2xcx9c3 mm after a long time use can be also predicted. As a result, a prediction of a maximum perimeter deviation of about 10 mm is necessary.
Therefore, in the above image forming device, due to the perimeter deviation of the intermediate transfer belt, the position of the bending member that presses the intermediate transfer belt becomes a barrack. For example, when the initial perimeter of the intermediate transfer belt is 950 mm (23xc2x0 C.), if the belt perimeter has a variation of 10 mm, the bending member moves by 7 mm.
Therefore, in the image forming device disclosed in Japanese Laid Open No. 2000-137386, when no other elements are disposed at a position opposite to the cleaning device, due to the variation of the belt perimeter of the intermediate transfer belt, the position of the pressing member (used as the bending member) is changed, and a deviation in the position relationship between the cleaning device and the intermediate transfer belt is created. The cleaning ability of the cleaning device for the residual toner gets worse.
Namely, in the image forming device, when the belt perimeter of the intermediate transfer belt is stretched, the position of the pressing member might be changed in a direction where the intermediate transfer belt and the cleaning device are separated. As described above, as the position of the pressing member might be changed in a direction where the intermediate transfer belt and the cleaning device are separated, the contact angle and the engaging amount between the cleaning device and the intermediate transfer belt are reduced.
In addition, in the above bending device, in order to stabilize the first transfer stage for transferring the toner image onto the intermediate transfer belt 10, the driving roller 14 is disposed at the downstream side of the first transfer device in the belt""s rotational direction, in general. Namely, the driving roller 14 is disposed at the downstream side of the first transfer device in the belt""s rotational direction, and therefore, the belt portion corresponding to the first transfer device becomes stretched side of the belt, so that the toner image transferred to the intermediate transfer belt in the first transfer stage can be stabilized. However, in this belt device, the belt portion corresponding to the secondary transfer device becomes a loose side. Therefore, to transfer the composite toner image onto the transfer paper might be unstable. One of the method to solve this issue is to make the bending roller 150 to possess function as a belt tension member, so as to provide a tension against the belt outer surface that is at the secondary transfer device""s downstream side in the belt""s rotational direction.
As the bending roller 150 is displaced due to the perimeter variation of the belt 10, for example, as shown in FIG. 14, a deviation in the position relationship between the cleaning blade 17a and the belt outer surface is created. This position deviation causes the reduction of the cleaning blade 17axe2x80x2s cleaning ability and the belt device""s life time. Namely, when the intermediate transfer belt 10 is deviated by the bending roller 150""s displacement in a direction where the belt 10 is separated from the cleaning blade 17a, the contact angle and the engaging amount between the belt 10 and the cleaning blade 17a are reduced. Therefore, in this situation, the cleaning ability for the residual toner on the belt 10 is reduced. On the other hand, when the intermediate transfer belt 10 is deviated by the bending roller 150""s displacement in a direction where the belt 10 is close to the cleaning blade 17a, the contact pressure between the belt 10 and the cleaning blade 17a increases. Therefore, in this situation, the wear of the belt outer surface is quick and the loading of the belt 10 during its rotation is increased, so that the life time of the belt device is reduced.
Furthermore, the position deviation of the belt does not only relate to the cleaning blade 17a. When the aforementioned position deviation occurs on the belt, somewhat adverse effect might impart on the acting member that provides certain action against the belt outer surface even though in the status that the predetermined position relationship with respect to the belt""s outer surface at the upstream side of the bending roller 150. For example, when the acting member is a coating member for coating a lubricant such as the zinc stearate etc on the belt outer surface, if the contact condition between the coating member and the belt outer surface is changed due to the belt""s position deviation, the lubricant cannot be uniformly coated on the belt outer surface. The other members that will be adversely affected by the belt""s position deviation are the charging device for charging the belt""s outer surface, the exposure device for exposing the belt""s outer surface, for example.
In addition, in the above description, the belt""s position deviation is created by the displacement of the bending roller 150. However, the position deviation can be also created by that belt is loosened by the driving roller 14 when the belt is driven to rotate. Therefore, in the belt device where the above bending roller 150 is disposed at the position corresponding to the belt loose side, even though the bending roller 150 does not displace, the loose belt might cause adverse effect on the other members.
In addition, in the above description, it states that the position deviation of the intermediate transfer belt 10 affect adversely on the acting members. However, this problem is limited to the above situation. For example, when the belt is the photoreceptor belt, if the deviation in the position relationship between the exposure device (used as the acting member) and the photoreceptor belt is created, to form a good latent image is damaged. In addition, when the belt is the paper transporting belt for transporting the transfer paper, if the deviation in the position relationship between the charging device (used as the acting member) and the paper transporting belt is created, the electrostatic adhesion of the transfer paper to the paper transporting belt is unstable. Furthermore, when the belt is the fixing belt for fixing the toner image on the transfer paper, if the deviation in the position relationship between the releasing-oil coating device (used as the acting member) and the fixing belt is created, unevenness in coating the oil onto the fixing belt might occur.
In light of the foregoing problems, it is an object of this invention to provide an image forming device, wherein even though the perimeter of the intermediate transfer belt is changed, a good cleaning ability for the intermediate transfer belt can be maintained.
It is another object of this invention to provide a belt device, wherein even though a position deviation of the belt occurs, the position relationship between the acting member and the belt outer surface can be maintained.
It is still another object of this invention to provide an image forming device using the above belt device to perform the image forming process.
According to the objects mentioned above, the invention provides an image forming device. The image forming device comprises an endless intermediate transfer belt, stretched by a plurality of rollers; a plurality of image supporters, disposed at positions opposite to the endless intermediate transfer belt; a plurality of image forming units, for forming toner images respectively on each of the image supporters; a first transfer device, for performing a first transfer stage, wherein each toner image formed on each image supporter is sequentially composed on the endless intermediate transfer belt at a first transfer section where the endless intermediate transfer belt and the image supporters are oppositely arranged; a secondary transfer device, for performing a secondary transfer stage, wherein a composite toner image transferred on the endless intermediate transfer belt at a secondary transfer section where the endless intermediate transfer belt and a transfer material are oppositely arranged; a bending member, for bending a toner image supporting surface of the endless intermediate transfer belt between the first transfer section and the secondary transfer section towards an inner surface side of the endless intermediate transfer belt; a cleaning device, disposed between the bending member and the secondary transfer section, for cleaning up the toner image supporting surface of the endless intermediate transfer belt; and an opposite member, disposed at a position opposite to the cleaning device to sandwich the endless intermediate transfer belt, and in contact with the inner surface of the endless intermediate transfer belt.
In the above image forming device, by using the opposite member, the toner image supporting surface of the intermediate transfer belt is regularly in contact with the cleaning device disposed between the bending member and the secondary transfer device. In this way, even though the position of the bending member is changed by the expansion or the contraction of the intermediate transfer belt, the deviation in the position relationship between the intermediate transfer belt and the cleaning device does not occur. Therefore, in the image forming device, the contact angle and the engaging amount between the cleaning device and the intermediate transfer belt can be more stable and a good cleaning ability for the intermediate transfer belt can be maintained.
The opposite member is disposed in a manner that the inner surface of the endless intermediate transfer belt is bent to the outer surface side of the endless intermediate transfer belt. In the above image forming device, by using the opposite member, the inner surface of the intermediate transfer belt is bent to the outer surface side of the intermediate transfer belt. In this way, the contact angle and the engaging amount between the cleaning device and the intermediate transfer belt can be more stable and a good cleaning ability for the intermediate transfer belt can be maintained.
The bending member can be a tension member for providing a tension against the endless intermediate transfer belt by a displacement of the bending member. In the above image forming device, by using the tension member as the bending member to provide a tension against the intermediate transfer belt, the belt running ability of the intermediate transfer belt that is in contact with the cleaning device can be stabilized, and therefore, a good cleaning ability for the intermediate transfer belt can be maintained. The tension member can use a roller that is rotated and is in contact with the outer surface of the intermediate transfer belt. In this situation, the degradation of the outer surface of the intermediate transfer belt can be suppressed to minimum, so that the belt running ability of the intermediate transfer belt can be stable.
Furthermore, in a status that the perimeter is minimum, the tension member has a maximum displacement to an outer surface side of the endless intermediate transfer belt, the endless intermediate transfer belt has a perimeter where a contact portion with respect to the opposite member is bent to the outer surface side.
In the above image forming device, the perimeter of the intermediate transfer belt can be minimized because of its tolerance, the use environment and the long time use. Even though the tension member has a maximum displacement to the outer surface side of the intermediate transfer belt, the contact portion corresponding to the opposite member is bent to the outer surface side. Therefore, in the image forming device, even though the perimeter is changed by the expansion and the contraction of the intermediate transfer belt, the contact angle and the engaging amount between the cleaning device and the intermediate transfer belt can be regularly stable and a good cleaning ability for the intermediate transfer belt can be maintained.
The opposite member can be a roller that is rotated and is in contact with the inner surface of the endless intermediate transfer belt. In the image forming device, by using the roller as the opposite member, the degradation of the outer surface of the intermediate transfer belt can be suppressed to minimum, so that the belt running ability of the intermediate transfer belt can be stable.
The invention further provides a belt device. The belt device comprises an endless belt; a driving roller for driving the endless belt to rotate in a predetermined direction; a supporting roller, for supporting the belt at a position of a loose side of the belt that is driven by the driving roller to rotates; a bending member, located at a downstream side of the supporting roller in the belt""s rotational direction, for bending an outer surface of the belt to an inner surface side of the belt; an acting member, disposed between the supporting roller and the bending member, maintaining a predetermined position relationship with respect to the outer surface of the belt to provide a predetermined action on the outer surface of the belt; and an opposite member, disposed at a position opposite to the acting member to sandwich the belt, and being in contact with the inner surface of the belt.
In the above belt device, since the belt inner surface is in contact with the opposite member, the position relationship between the acting member and the belt outer surface can be maintained. In this way, even though the bending member is displaced by the belt""s expansion or contraction or the belt is loose at the beginning of driving the belt, the deviation in the position relationship between the acting member and the belt outer surface does not occur.
In the above belt device, the opposite member is in contact with inner surface of the belt, such that a winding angle of the belt with respect to the supporting roller is set at an angle capable of separating a sheet that is transported along the outer surface of the belt of the supporting roller""s upstream side in the belt""s rotational direction from the outer surface of the belt.
In addition, the belt device further comprises a belt tension applying member for providing a predetermined tension against the belt. The belt tension applying member is disposed at a position where the winding angle of the belt with respect to the supporting roller is not changed by utilizing a displacement of the belt tension applying member.
In the above belt device, the bending member also functions as the belt tension applying member. Alternatively, the acting member can be a cleaning device for cleaning the outer surface of the belt. The cleaning device can be a blade in contact with the outer surface of the belt. In addition, the cleaning device can also be a fur brush that is able to rotate and is in contact with the outer surface of the belt.
In the above belt device, the opposite member is disposed at a position to press the inner surface of the belt, even though the belt has a maximum contraction and the bending member displaces to the outer surface side of the belt.
In the above belt device, preferably, the bending member can be a roller, the opposite member can be a roller, and the belt tension applying member can be also a roller.
In the above belt device, the belt can be a transferring/transporting belt, for transporting a recording medium having an image recorded thereon, and for transferring the image, which is formed on an image supporter disposed along the outer surface of the belt, onto the recording medium.
In the above belt device, the belt can be an intermediate transfer belt. The image on the image supporter disposed along the outer surface of the belt is first transferred, and the first transferred image is transferred on the recording medium that is fed to opposite the outer surface of the belt.
The belt, the driving roller, the supporting roller, the bending member, and the belt tension applying member are integrally contained within a frame, wherein the frame is detachably installed at a predetermined position in an image forming device that is used to form an image on a recording medium.
In addition, the belt device further comprises a driving force transmitting device for transmitting a driving force form a driving source installed in a main body of the image forming device to the driving roller, as the frame is installed at the predetermined position in the image forming device.
The invention further provides an image forming device, which comprises at least one image supporter, for supporting an image; at least one image forming means, for forming the image on the image supporter; and a transferring device, having a belt device, wherein the belt device has an endless type belt, and the endless type belt is stretched by a plurality of rollers and is driven to rotate, and the belt device has a structure as described above.
In the above image forming device, the image means further comprises a plurality of developing device capable of sequentially overlapping toner images with different colors onto the image supporter. In addition, the image supporter and the image forming means forms one image forming unit, and a plurality of the image forming units are arranged along the endless type belt of the belt device.